As the integration of LSI is improved, an LSI referred to as an SoC (System on Chip) which is a microcomputer configured as a chip configuring a system on a silicon has been realized. The SoC mounts a memory inside the chip in many cases, and the storage capacity of a memory to be mounted thereon has been increased year after year.
In an ASIC (Application Specific Integrated Circuit) which is realized as an SoC and is designed and manufactured for a certain purpose, there are cases in which electric power saving design referred to as a voltage island is performed in order to reduce electric power consumption. The voltage island divides the circuit in the ASIC into a plurality of modules, controls a power gate circuit, and is capable of independently switching on and off of the electric power source for each divided individual modules. Further, the electric power source not being used is switched off, whereby the leak current of such module can be prevented. By using such technique, the electric power source of the most part of the circuit not being needed can be turned off, whereby the leak current of ASIC can be suppressed to the minimum amount.